The present application claims priority under 35 U.S.C. xc2xa7119 to Korean Application No. P2002-72436, filed Nov. 20, 2002, the entire disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates in general to a magnetron which generates a microwave and, more particularly, to a magnetron and a method for joining magnetron components which can prevent vacuum leakage caused by defective joining between components.
2. Background of the Related Art
In general, a magnetron can be used in devices such as microwave ovens, plasma lighting apparatuses, dryers, and other microwave systems.
When power is applied to a magnetron, the magnetron, one of a plurality of vacuum tubes, emits thermal electrons from a cathode, which produces a microwave by interaction between a strong electric field and a magnetic field. Thus produced, the microwave is transmitted outside of the magnetron through all antenna feeder and is used as a heat source for heating all object.
The magnetron is provided with an anode having all anode cylinder and an anode vain, a cathode having a filament, a condenser, a choke coil, and leads for applying) power to the filament. A pair of magnets, a pair of pole pieces, and a yoke form a magnetic circuit. An antenna feeder and an antenna cap transmit a generated microwave outside of the magnetron.
A portion of the magnetron needs to be maintained at a vacuum. The components of this portion of the magnetron are joined together in a way that greatly affects performance of the magnetron. These components need to be joined sufficiently tightly that air cannot pass through the joints. The joints are generally made of a ceramic material component and a metal material component. To maintain proper performance of the magnetron, a technique is required for precise joining of the metal component to the ceramic component.
FIG. 1 schematically illustrates joints of filament leads and external leads of a related art magnetron. FIG. 1 shows a pair of filament leads 15 connected to a filament 11 and a pair of external leads 22 connected to a choke coil (not shown), a lower seal 14 formed of a metal forming a part of the vacuum space, and a ceramic stem 21.
Referring to FIG. 1, an upper end shield 12 and a lower end shield 13 are provided at the top and bottom, respectively, of the filament 11. The pair of filament leads 15 is provided under the lower end shield 13. The lower seal 14 maintains an airtight lower space on the inside of an anode cylinder (not shown). The ceramic stem 21 is provided under the lower seal 14. The external leads 22 are connected to the choke coil and are fitted to pass through an inside of the ceramic stem 21.
A terminal plate 23 (not shown) is provided on top of the ceramic stem 21 for connecting the pair of filament leads 15 to the pair of external leads 22. More specifically, the terminal plate 23 is made of two pieces which are not in contract. One of the filament leads 15 and one of the external leads 22 are connected to one of the pieces of the terminal plate 23. The other one of the filament leads 15 and the other one of the external leads 22 are connected to the other one of the pieces of the terminal plate 23. Thus, the pair of filament leads 15 and the pair of external leads 22 are connected from opposite sides through the two pieces of the terminal plate 23.
Because many components are joined in fabricating the foregoing related art structure, the fabricating process is very complicated. Direct brazing on the surface of the ceramic stem 21 is not possible in brazing the terminal plate 23 with a top surface of the ceramic stem 21. Because an additional metal film is formed on the top surface of the ceramic stem before joining the terminal plate 23 by brazing, metalizing is required to form a metal film on a joining surface of the ceramic stem 21.
Generally, because direct joining is not possible by general brazing methods, to more accurately join a metal component and a ceramic component, the metal component and the metal film part are joined by brazing after a metal film is formed on the ceramic component. That is, because the direct joining of the metal and the ceramic are not possible in the related art, a metalizing process is carried out for forming the metal film on the surface of the ceramic component to join metals.
This metalizing is a process in which a paste containing molybdenum Mo and manganese Mn is applied to a surface of the ceramic, and heated to an elevated temperature higher than 1600xc2x0 C. to form the metal film on the surface of the ceramic. However, the metalizing not only complicates the fabrication process, it also increases the fabrication cost of the structure, since an additional furnace is required.
Moreover, the joining of filament leads 15 to one side of the terminal plate 23 and the joining of the external leads 22 to the other side of the terminal plate 22 requires a complicated process, which reduces the productivity of the structure.
Furthermore, the terminal plate 23 is thin and, therefore, susceptible to deformation, causing defects in the brazing of the terminal plate 23 with the ceramic Stem 21. This also causes difficulty in correctly positioning the filament leads 15, resulting in poor reliability and performance of the magnetron.
Accordingly, the present invention is directed to a magnetron that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a magnetron which can prevent vacuum leakage caused by defective joining between components.
Another object of the present invention is to provide a magnetron in which components can be assembled easily.
Yet another object of the present invention is to provide a method for joining components of a magnetron which can improve joining and assembly of the components.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other a advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the magnetron includes an anode having an anode cylinder and anode vanes; a cathode having a filament; a condenser, a choke coil, and a plurality of leads for providing power to the filament; a plurality of magnets and pole pieces, and a yoke for forming a magnetic circuit; an antenna feeder and an antenna cap for transmitting a generated microwave outside of the magnetron; and a plurality of joints formed of a joining material between a metal component and a ceramic component of the magnetron, wherein the joining material is diffused between the metal component and the ceramic component, to infiltrate into an inner part of the ceramic component directly, thereby joining the metal and ceramic components.
The joint is provided at a part between an upper seal on top of the anode cylinder and an upper ceramic at a bottom of the antenna cap. The joint is further provided at a part between an exhaust pipe supporter of a metal, which supports an exhaust pipe that surrounds a top end of the antenna feeder, and an upper ceramic under the antenna cap. The joint is further provided at a part between a lower seal under the anode cylinder and a ceramic stem provided to permit pass of a plurality of leads.
The joint is further provided to an inside of an insertion hole in the ceramic stem the leads pass therethrough. The joint is further provided at a part between a filament lead connected to the filament and the external lead connected to the choke coil. The external lead has a diameter the same as or greater than a diameter of the filament lead, the external lead has a recess in an end thereof, for insertion of an end of the filament lead. The filament lead has a recess in an end thereof The external lead has a tip at all end thereof for insertion into the recess.
The joining material is an alloy of silver-copper-additive. The additive has a content of 1 to 10% in weight. The joining material has a composition ratio of silver:copper:additive in weight of 60 to 80:10 to 39:1 to 10. The additive is a material selected from at least one of titanium, tin, and zirconium, wherein the joining material may have a composition ratio of silver:copper:titanium of 60 to 80:10 39:1 to 10, a composition ratio of silver:copper: tin of 60 to 80:10 to 39:1 to 10, a composition ratio of silver:copper:zirconium of 60 to 80:10 to 39:1 to 10, or a composition ratio of silver:copper:titanium of 60 to 68:27 to 33:2 to 5.
In another aspect of the present invention, there is provided a method for joining magnetron components comprising the steps of (a) providing a joining material at parts to be joined inclusive of parts between a metal component and a ceramic component, and between a filament lead and an external lead, (b) exposing the joining material to a preset temperature and a preset environment, for diffusing the joining material into the part to be joined, to infiltrate into an inner part of the ceramic component, and (c) cooling down the joining material, to join the part to be joined.
The step (a) includes the steps of (a1) providing the joining material at a part between a lower seal under the anode cylinder and a ceramic stem, (a2) providing the joining material at a part between an upper seal on top of the anode cylinder and an upper ceramic under the antenna cap, (a3) providing the joining material at parts between an insertion hole in the ceramic stem and a filament lead passed through the insertion hole, and between the insertion hole and an external lead passed through the insertion hole, and (a4) providing the joining material at a part between the filament lead and the external lead.
The step (a3) includes the steps of rolling a sheet of the insertion material rolled into a cylindrical form, and inserting into the insertion hole, to provide the joining material to an inside wall surface of the insertion hole, and inserting the filament lead and the external leads into the insertion hole from opposite sides of the insertion hole through an inside of the cylindrical joint material. The step (a3) includes the steps of inserting a cylindrical form of the joining material already prepared into the insertion hole, to provide the joining material to an inside wall surface of the insertion hole, and inserting the filament lead and the external leads into the insertion hole from opposite sides of the insertion hole through an inside of the cylindrical joint material.
The step (a4) includes the steps of forming a depth of recess in an end of the external lead, placing the joining material in the recess, and inserting an end of the filament lead into the recess. The step (a4) includes the steps of forming a recess in an end of the filament lead, and forming a tip at an end of the external lead, placing the joining material in the recess, and inserting the tip into the recess.
The step (a) includes the step of providing a joining material to a thickness of about 50-200 xcexcm.
The step (b) includes the step of exposing the joining material to a temperature range of about 800-1000xc2x0 C., for diffusing, and infiltrating the joining material, wherein the step (b) includes the step of exposing the joining material to a vacuum, for diffusing, and infiltrating the joining material, when the vacuum is about 1xc3x9710xe2x88x923 to 1xc3x9710xe2x88x925 torr. Or alternatively, the step (b) includes the step of exposing the joining material to hydrogen gas, for diffusing, and infiltrating the joining material, or the step (b) includes the step of exposing the joining material to argon, for diffusing, and infiltrating the joining material.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.